A small vehicle powered by electricity from batteries or other means offers the solution to city traffic congestion and pollution problem. In fact, very high percentages of vehicles driving on the highway or city streets, especially in the United States, have no more than two occupants. This means that these low occupied vehicles moving on the streets can be replaced by two seat smaller vehicles to lower fuel consumption and lower the pollution level. However, small vehicles typically are not safe to drive on the streets where a lot of big trucks, big SUVs and regular size sedans are also sharing. To make small vehicles safer to drive on the streets, special design for collision prevention should be implemented up to a level that the general public can accept before we see small two seat vehicles widely show up on the streets.
For example, a U.S. patent application US20070164583 presents a design in which vehicle body can be expanded to a bigger size for collision protection during highway driving and shrink back to small size for narrow street driving. The drawback of this design is that, while the vehicle body can be expanded bigger to provide more cushion, the collision protection may not strong enough and it is difficult to make the shell of the vehicle looks appealing.
U.S. Pat. No. 7,780,197 presented a way to extend the front wheels and rear wheels by using telescoping tube structure. The drawbacks of this design is that it still uses a single steering mechanism with rods connecting to both front wheels, thus the complex nature of the mechanism for a heavy farm tractor will be difficult to maintain the rigidity of the structure. The tube axle will also have difficulty to bear the load of the heavy tractor because when it expands outward, the portion left in the frame tube will be very limited because the frame tube needs to contain left and right hand axle tubes, particularly for the rear axle due to the existence of the differential gear. It is easy to see that such expandable axle design is not possible for a small vehicle having a very narrow track such as 42″ to begin with.
European patent application EP1908674A1 further disclosed a design using hydraulic cylinders to achieve the expansion and retraction of the four wheels of a vehicle.
On U.S. Pat. No. 8,205,892 Mackin et al. disclosed a method to use toe-in and toe-out of wheels rolling on ground as driving forces to change hydraulic equipped vehicle axles for changing the track width of a vehicle.
However, changing vehicle wheel tracks is not only difficult to design, given that normal commercial vehicles typically have rack and pinion mechanism for steering function and transmission axles coupled with differential gear assemblies for rear or front axle to deliver power, there is no good reason to have such capability for most of them because they already have wheel tracks wide enough to occupy major portion of the lanes in most highways anywhere. Small cars, on the opposite, can use such capability to make it safer and more stable to drive because there is room to expand the wheel tracks for being small.
Considering that most high speed race cars have a design that typically having a small chassis supported by four wheels which span much wider track width than the width of the chassis, it offers a clue to make a smaller car very stable to drive in high speed and at the mean time it also offers some protection for the chassis from the wider track of four wheels, as well as passengers inside the cars. This idea is particularly useful for developing a small electric vehicle which does not need as much electric power as a traditional vehicles having capacity of four or five passengers. Therefore, it is intuitively true that a design for a small vehicle seating two persons in tandem which is capable of changing its track width to a narrow track for narrow street driving and wide track width for high speed driving would be an ideal small electric car in the near future. A similar design for such purpose is shown, for example, in U.S. Pat. No. 8,746,388. The major disadvantages of design in the above mentioned patent is that it widens the track of front wheels only, not front and rear wheels at the same time and is thus not able to provide as much collision protection and stability as desired. Another disadvantage is that the mechanism to support the track width change, combined with originally equipped suspension and steering mechanism, becomes very complicated and the rigidness of such structure could face big challenge during high speed driving in addition to questionable durability problem.
Electric cars using batteries or fuel cells are gradually considered as a way to solve pollution problem in urban area. However, battery power is still very expensive in terms of reasonable driving range between recharges for a normal five seat sedan. To make electric popular among all drivers, smaller cars with enough collision protection is the way to go; daily commute to work does not need a full sized car.
The purpose of current invention is to provide a coaxial multi-member mechanism for using as both front and rear axles in an small electric vehicle such that its four wheels can expand to a wide wheel track if it is to be driven with high speed on the highway for safer and more stable condition; and retract to narrow wheel track as a small car to tour in narrow streets.
Further more, the intended application of the invention is for electric cars with no emission, small size of such vehicles makes them particularly easy to solve parking problem—they don't need to park in conventional parking space. They can even be driven into elevator and parked in the lobby area of a big building, provided that the building is equipped with elevator big enough to carry the vehicles to all levels in the building, thus relieve a lot of city parking problems.